The invention relates to measuring pick-ups or transducers, especially strain gage force transducers and to a method for adjusting such transducers having at least one strain gage applied to a spring body. The adjustment is accomplished by activating further strain gage components. The invention also relates to foil strain gages suitable for use in the present adjustment method.
U.S. Pat. No. 3,737,827 describes, for example, an adjustment method for strain gages. Particularly FIG. 4 of said U.S. patent and the respective description of FIG. 4 shows that creep of a strain gage may be adjusted in a strain gage transducer of the type mentioned above by providing the strain gage with additional creep compensating strain gage components which form loops in the grid structure of the strain gage. These additional strain gage loops are connected for activation to corresponding terminals of the strain gage.
A measuring transducer or pick-up has been suggested in which strain gage arrangement may be adjusted relative to creep, relative to its resistance, as well as relative to torque load errors in that further strain gage components connected to the strain gage arrangement may be activated by opening conductor sections which prior to such opening short circuit the additional strain gage components.
It is also generally known that measuring pick-ups or transducers having at least one strain gage applied to a spring body, especially when force transducers are involved, are subject to errors resulting from nonideal, off-center load applications. These errors result when the force to be measured is applied to the transducer at a point off-center relative to an optimal point of load application. Such off-center load applications influence the deformation of the spring body in a manner which is hard to control. Thus, even small off-center load applications relative to the optimal point of load application, result in substantial bending moments in an axially loaded, cylindrical measuring rod, whereby a correspondingly complex deformation characteristic is caused.
Further, additional output errors may result because of force components present in addition to the force component effective in the optimal measuring direction or rather effective in the optimal point of load application. Such additional force components also cause loads in the spring body of the transducer, thereby influencing the output reading. In theory such errors are compensated by multiple strain gage arrangements on the spring body and by interconnecting such multiple strain gages in a Wheatstone bridge circuit. However, practical experience has shown that such theoretical compensation cannot be achieved completely so that erroneous output readings as a result of error loading must be taken into consideration at least to a certain extent. In order to keep these error causing effects as small as possible, attempts have been made to eliminate erroneous loading, for example, by carefully locating the load application point in the spring body of the transducer. However, this approach is subject to physical and economical limitations.